1. Field of the Invention
The present invention generally relates to wireless local area networks and portable or mobile communications equipment such as telephones, computers, personal digital assistants, pagers, and data collection and roaming terminals, as well as stationary equipment such as fixed access points or base stations and, more particularly, to improvements in holding, shielding, grounding and transmitting/receiving radio frequency signals for a communications equipment card used in such mobile and/or stationary equipment.
2. Description of the Related Art
Wireless local area networks use radio frequency (RF) communications channels to communicate between communications equipment. Each equipment may be a portable or mobile terminal or station, such as a telephone, computer, personal digital assistant, pagers, and data collection and roaming terminal, or a stationary terminal or station, such as a fixed access point or base station. Typically, a multitude of mobile terminals communicate with a plurality of stationary terminals such as host computers. The stationary terminals are, in turn, connected by a wired or wireless channel to a network infrastructure.
Wireless and RF protocols are known which support the logical interconnection of portable terminals having a variety of types of communication capabilities to stationary terminals. The logical interconnections are based upon an infrastructure in which at least some of each of the portable terminals are capable of communicating with at least two of the stationary terminals when located within a predetermined range therefrom, each portable terminal being normally associated and in communication with a single one of such stationary terminals. Based on the overall spatial layout, response time, and loading requirements of the network, different networking schemes and communications protocols have been designed so as to most efficiently regulate the communications.
One such protocol is set forth in the IEEE Standard 802.11 entitled xe2x80x9cWireless LAN Medium Access Control (MAC) and Physical Layer (PHY) Specificationsxe2x80x9d available from the IEEE Standards Department, Piscataway, N.J., (hereinafter, the xe2x80x9cIEEE 802.11 standardxe2x80x9d). The IEEE 802.11 standard is directed to wireless local area networks, and in particular specifies the MAC or the data link layer and the PHY or physical link layer. These layers are intended to correspond closely to the two lowest layers of the ISO Basic Reference Model of OSI, i.e., the physical layer and the data link layer. The IEEE 802.11 standard permits communications, at 1 Mbps, 2 Mbps and higher data rates, a medium access technique similar to carrier sense multiple access/collision avoidance (CSMA/CA), a power-save mode for battery-operated mobile stations, seamless roaming in a full cellular network, high throughput operation, diverse antenna systems designed to eliminate xe2x80x9cdead spotsxe2x80x9d, and an easy interface to existing network infrastructures.
The current implementations of commercial wireless local area networks utilize a transceiver operating in the 2.4 to 2.4835 GHz spread spectrum band which is the industrial, scientific, and medical (ISM) band allocated for unlicensed use by the U.S. Federal Communications Commission. The current systems utilize one of two basic types of spread spectrum modulation: direct-sequence and frequency-hopping.
In a direct-sequence spread spectrum (DSSS) system, each binary bit of data in a data signal is spread over each of 11 discrete frequency channels at the same time, i.e., an 11-bit pseudorandom noise (PN) code. The data of each user is coded using a different PN code so that the signals of different users are orthogonal to each other. Thus, another user""s signal is merely interpreted as noise. The IEEE 802.11 standard provides two modulation formats and data rates in the DSSS systemxe2x80x94a basic access rate using differential binary phase shift keying (DBPSK) modulation operating at 1 Mbps, and an enhanced access rate using differential quadrature phase shift keying (DQPSK) modulation operating at 2 Mbps.
In a frequency-hopping spread spectrum (FHSS) system, each binary bit of data in the data signal is associated with a group of distinct xe2x80x9cchipsxe2x80x9d, or discrete signal frequency output, in different parts of a frequency band, with a minimum hop of at least 6 MHz (in North America/Europe). The chipping pattern or hopping sequence is a pseudo-random sequence uniformly distributed throughout the band and set forth in the IEEE 802.11 standard. Each access point executes a unique hopping pattern across 79 non-overlapping frequencies at a rate of one hop every 100 milliseconds. There are three sets of hopping patterns specified in the IEEE 802.11 standard for North American/European operations, with each set containing 26 sequences. The sets are selected to minimize the possibility of interference. The RF modulation technique used in the FHSS system is 2-level or 4-level Gaussian-filtered frequency shift keying (GFSK). Frequency-hopping spread spectrum systems are currently preferred over direct sequence for most applications by the majority of users as they allow increased capacity and decreased interference. The FHSS system hops over channels with an effective raw data rate of 1 Mbps or 2 Mbps. Current commercial systems can typically cover from an area of 25,000 to 70,000 square feet with a process gain of 10 dB. The relatively low power output used in such systems is a consequence of limits placed by regulatory agencies. Power output standards currently in effect limits the power output to either 100 mW, 230 mW, or 500 mW depending on the country.
In a spread spectrum system, one can multiplex users by assigning them different spreading keys. Such a system is called a code division multiple access (CDMA) system. Most wireless local area network products are not CDMA systems since users belonging to the same wireless local area network utilize the same spreading key. Instead, as noted above, the media access protocol (MAC) set forth in the IEEE 802.11 standard provides that use access to the channel is multiplexed in time using nearly the same Carrier Sense Multiple Access (CSMA) protocol as in the Ethernet.
Each of the aforementioned terminals utilize a communications equipment card which essentially comprises a radio frequency transceiver circuit for implementing the desired RF protocol, and an antenna, especially the classical xcex/4 monopole antenna as typified by the whip antenna. For increased miniaturization and sensitivity to electro-magnetic fields, inverted L- and F-antennas have been proposed to replace the monopole antenna.
The known antennas are connected to the transceiver circuits by being mounted on printed circuit boards that carry the circuits, by being loosely connected by cables or end caps, or by being encapsulated in shielded housings. Such methods are disadvantageous because they increase the occupied space factor and are therefore unsuitable for applications where a high degree of miniaturization is desired.
Accordingly, it is a general object of this invention to provide a highly suitable, miniaturized communications equipment component capable of performing multiple functions previously performed by multiple components.
Still another object of the present invention is to enable a single component to hold a radio frequency communications card, to shield the card from electro-magnetic interference, to transmit/receive radio frequency signals with a built-in antenna, and to serve as a ground plane for the antenna.
A still further object of the present invention is to reduce manufacturing and assembly costs for such components.
In keeping with the above objects and others which will become apparent hereafter, one feature of the present invention resides in a component for a radio frequency communications card, comprising a holder constituted of an electrically conductive material, such as sheet metal, for holding and shielding the card from radio frequency interference. The holder has a main portion lying in a plane which extends over the card and a pair of side portions integral with the main portion and extending over the side edges of the card. The main and side portions bound a compartment in which the card is slidably received and held. An end portion abuts against a leading edge of the card in a fully received, held position for the card. A plurality of mounting portions on the side portions are used for fixing the position of the holder in a communications equipment.
The component includes a built-in antenna constituted of the same material as, and being of one-piece with, the holder, and is operative for transmitting/receiving radio frequency signals to and from the card. The antenna is formed from the main portion itself. Specifically, an antenna portion is cut or stamped out of the main portion, but not completely removed therefrom. The antenna portion is bent out of the plane of the main portion and leaves behind a cutout that extends through the main portion. Preferably, the antenna portion has a first part extending generally perpendicularly to the main portion, a second part extending generally parallel to the main portion, and a feeding point connected to the main portion and to the second part, thereby configuring the antenna as an F-antenna.
The holder includes a grounding contact for grounding the holder and enabling the plane of the main portion to serve as a ground plane for the antenna. At least one of the side portions and the end portion, and preferably each of the side and end portions of the holder, is provided with the grounding contact which extends along the respective side and end portion and makes contact with a grounded area on the card.
In the preferred embodiment, two F-antennas are formed side-by-side in the main portion. A resilient tongue between the antennas resiliently bears against the card for a more secure holding and grounding of the card.
The novel features which are considered as characteristic of the invention are set forth in particular in the appended claims. The invention itself, however, both as to its construction and its method of operation, together with additional objects and advantages thereof, will be best understood from the following description of specific embodiments when read in connection with the accompanying drawings.